What is the distribution of normal saline (0.9% sodium chloride solution)?

From the Guidelines

Normal saline, a 0.9% sodium chloride solution, is primarily distributed throughout the extracellular fluid compartment of the body, with approximately 75% of the infused volume remaining in the intravascular space for about 30-60 minutes before redistributing to the interstitial space. When administered intravenously, the distribution of normal saline occurs because it has the same osmolarity (308 mOsm/L) as blood plasma, making it isotonic 1. The sodium and chloride ions cannot freely cross cell membranes, so they remain predominantly in the extracellular space, pulling water with them through osmotic pressure. This explains why normal saline is effective for short-term intravascular volume expansion but requires continued administration for sustained effect. In clinical practice, this distribution pattern makes normal saline suitable for treating mild to moderate dehydration, replacing fluid losses, and as a vehicle for medication administration, though it may not be ideal for long-term volume maintenance due to its relatively rapid redistribution out of the vascular space. Some studies suggest that the initial fluid therapy should be directed toward expansion of the intravascular and extravascular volume and restoration of renal perfusion, using isotonic saline (0.9% NaCl) at a rate of 15–20 ml/kg body wt/h or greater during the 1st hour 1. However, the most recent and highest quality study 1 provides more detailed guidance on the distribution and use of normal saline in clinical practice. Key points to consider when using normal saline include:

• The rate of infusion, which depends on the state of hydration, serum electrolyte levels, and urinary output
• The need to correct serum sodium levels for hyperglycemia
• The importance of monitoring serum osmolality and frequent assessment of cardiac, renal, and mental status during fluid resuscitation to avoid iatrogenic fluid overload. In summary, the distribution of normal saline is primarily extracellular, with a significant portion remaining in the intravascular space for a short period before redistributing to the interstitial space, making it suitable for short-term volume expansion and other clinical applications, as supported by the most recent evidence 1.

From the Research

Distribution of Normal Saline

The distribution of normal saline (0.9% sodium chloride solution) is a crucial aspect of fluid resuscitation in various medical settings.

• Normal saline is commonly used for fluid resuscitation in critically ill patients, including those with septic shock 2, 3.
• The volume of normal saline required for resuscitation can vary depending on the patient's condition, with some studies suggesting that up to 110 mL/kg may be required in the first hour for successful fluid resuscitation in children with septic shock 2.
• Normal saline has been compared to other fluid solutions, such as balanced crystalloids, in terms of its effects on patient outcomes, including mortality and incidence of acute kidney injury (AKI) 3, 4.
• Some studies have found that normal saline may be associated with a higher incidence of pulmonary edema compared to other fluid solutions, such as albumin or hetastarch 5.
• The choice of fluid solution for resuscitation may depend on the individual patient's condition, with some studies suggesting that balanced crystalloids may be preferred in certain situations, such as in patients with non-traumatic brain injury 4.
• In pediatric patients, normal saline is commonly used for fluid resuscitation, but there is a trend towards the use of balanced electrolyte solutions, and prospective studies are needed to compare the effects of these solutions in this population 6.

Key Findings

• Normal saline is widely used for fluid resuscitation in critically ill patients.
• The volume of normal saline required for resuscitation can vary depending on the patient's condition.
• Normal saline has been compared to other fluid solutions in terms of its effects on patient outcomes.
• The choice of fluid solution for resuscitation may depend on the individual patient's condition.
• Prospective studies are needed to compare the effects of normal saline and balanced electrolyte solutions in various patient populations, including pediatric patients 2, 3, 5, 4, 6.